1. Field of the Invention
The present invention relates in general to a semi-conductor on insulator material and process of making same and, more particularly, to a monocrystalline germanium film on an .alpha.-alumina substrate.
2. Description of the Prior Art
Semiconductor on insulator technology is used for complementary circuits and applications where a high density of devices is used and latch up needs to be controlled. Some of these materials also show good resistance to radiation. To date, most of the semiconductor on insulator technology is based on silicon coatings on a sapphire substrate (SOS). For example, U.S. Pat. No. 4,442,178 describes a process of forming a silicon layer with an index plane of (100) on a single crystal sapphire substrate with an index of plane (1102). U.S. Pat. No. 3,589,936 discloses the growth of single crystal germanium of (111) orientation on the basal (0001) plane of a sapphire substrate.
Germanium is known to grow on sapphire using chemical vapor deposition, chemical reactions, and recrystallization techniques. However, the limitations incurred in these methods are severe, since the growth of single crystal germanium on sapphire has been unsuccessful without the incorporation of substantial amounts of dopants. For example, U.S. Pat. No. 3,589,936 discloses growing crystalline germanium on the sapphire basal (0001) plane, only when the source germanium was heavily doped with arsenic or phosphorous.
U.S. Pat. No. 3,433,684 discloses a process of forming a germanium film by chemical vapor deposition on a sapphire substrate by heating the substrate to between 500.degree.-800.degree. C. and flowing GeH.sub.4 over the substrate. The (111) plane of the germanium is deposited on the basal plane of the sapphire substrate. However, the basal plane of sapphire is not generally used in the SOS technology. Consequently, it is desirable to have a process of depositing monocrystalline germanium on the (1102) plane of sapphire, which, in the case of analogous silicon on sapphire films, is used in high radiation resistant circuits.
It is desirable to have the ability to produce an undoped single crystalline germanium film on a sapphire substrate due to the sometimes desirable electrical properties of the undoped monocrystalline germanium. It is also desirable to have a process in which doped or undoped monocrystalline germanium (110 plane) can be formed on the commercially more important r-plane [or (1102)] of .alpha.-alumina substrate such as sapphire.